The methods using supercritical ammonia are proposed as the process for forming a bulk monocrystalline gallium nitride so as to lower the temperature and the pressure for a growing step. One of the methods is to grow GaN crystal by synthesizing ammonia containing alkali metal amide (KNH2 or LiNH2), where Gallium is used as a feedstock, by setting the reaction temperature below 550° C., pressure below 5 kbar, and the resultant grown crystal is 5 μm. [“ammono method of BN, AlN, and GaN synthesis and crystal growth” R. Dwilinski et al., Proc. EGW-3, Warsaw, Jun. 22–24, 1998, MRS Internet Journal of Nitride Semiconductor Research] Another method is to recrystallize gallium nitride by using commercially available GaN powder. [“Crystal Growth of gallium nitride in supercritical ammonia”, J. W. Kolis et al., J. Cryst. Growth 222, 431–434 (2001)]. However, the former is a method using gallium metal as a feedstock and the reaction control is difficult. Although the latter is a recrystallizing method using GaN as a feedstock, only GaN crystal about 0.5 mm was obtained and no bulk monocrystalline was obtained. We believe this was caused because neither chemical transport in the supercritical solution nor growth on a seed was seen. Gallium nitride as a raw material does not exist in nature, differently from quartz crystal, therefore it is difficult to supply.